Aromatic hydrocarbons such as benzene and naphthalene can be obtained by separating from petroleum and coal tar. These aromatic hydrocarbons contain sulfur compounds as impurities. These aromatic hydrocarbons are used as basic raw materials for various petrochemicals or intermediate materials. When these products or intermediate materials are manufactured, sulfur compounds may act as a catalyst poison. Therefore, in many cases, the aromatic hydrocarbons must be desulfurized to a sulfur content of 1 ppm or less, preferably 0.5 ppm or less, and more preferably 0.1 ppm or less. However, because sulfur compounds contained in these aromatic hydrocarbons are aromatic sulfur compounds such as thiophenes, benzothiophenes, and dibenzothiophenes having boiling points and properties similar to the aromatic hydrocarbons, it is not easy to precisely separate them by distillation.
A method for removing the sulfur compounds by adsorption using a physical adsorbent without a reaction has been studied (Patent Document 1). However, removing sulfur compounds in hydrocarbon oils with a high aromatic hydrocarbon content by adsorption is not easy, particularly when the content of the sulfur compound is low. A method for removing the sulfur compounds as sulfur by chemisorption using a sorbent accompanying a reaction has also been researched (Patent Document 2). However, the document refers to investigation of desulfurization of naphtha with a low aromatic content and does not refer to thiophenes, benzothiophenes, and dibenzothiophenes. The desulfurization reaction in hydrorefining not only requires a high operating cost and high equipment cost due to the reaction using hydrogen at a high temperature under high pressure, but also contains problem of impurities produced due to hydrogenation or decomposition of aromatic hydrocarbons themselves. Production of impurities is significant particularly when the content of sulfur compounds is small. Oxidation desulfurization using an oxidizer requires complicated equipment, a high operating cost and equipment cost due to need for phase separation in addition to the use of an oxidizer such as hydrogen peroxide and an acid catalyst. A method for removing sulfur compounds by homopolymerization or decomposition by adding anhydrous aluminum chloride is also known (Patent Documents 3 and 4). The method has problems that not only the use of anhydrous aluminum chloride requires a high operating cost and equipment cost, but also the rate of desulfurization is low due to the low rate of homopolymerization or decomposition.
[Patent Document 1] Japanese Patent Application No. 2003-77594
[Patent Document 2] Japanese Patent Application Laid-open No. 2-132186
[Patent Document 3] Japanese Patent Publication No. 4747021
[Patent Document 4] Japanese Patent Application Laid-open No. 63-57539